1. Field of the invention
The present invention relates, in general, to a multi-wavelength light receiving element and a method of fabricating the same and, more particularly, to a multi-wavelength light receiving element, which is capable of detecting rays having various wavelengths so as to be useful as a light pickup in optical reproduction devices, such as CDs, DVDs, and BDs, and a method of fabricating the same.
2. Description of the Prior Art
In accordance with the recent development of the media industry, the demand for high-capacity storage devices is growing. Hence, compact discs (CD), which adopt a digital sampling method, have been used as a substitute for magnetic tapes conventionally used to record and replay music. Of the compact discs, a CD media, which has a diameter of 12 cm and uses a wavelength of 780 nm, achieves a capacity of 650 MB.
However, digital versatile discs (DVD), which use a wavelength of 650 nm, have been developed to meet the increased demand for digital videos, thereby realizing a capacity of about 4.7 GB. It is possible to record images, which have a quality that is on the level of super density (SD), for 2 hours or more using the DVDs.
Additionally, a photodiode, that is, a light receiving element, which converts received optical signals, having various wavelengths, into electrical signals, and a photodiode integrated circuit (PDIC), which amplifies the electrical signals generated from the light receiving element, have been studied so as to simultaneously accommodate CDs and DVDs.
FIG. 1 is a sectional view of a conventional 2-wavelength light receiving element, which is capable of simultaneously accommodating CDs and DVDs. FIG. 2 is a graph showing intensities of rays, having various wavelengths, as a function of a distance from a surface of a silicone substrate.
As shown in FIG. 1, the conventional 2-wavelength light receiving element comprises a silicon substrate 11, a heavily-doped P-type buried layer 12, a P-type epitaxial layer 13, an N-type epitaxial layer 14, and a heavily-doped N-type layer 15. The heavily-doped P-type buried layer 12, the P-type epitaxial layer 13, the N-type epitaxial layer 14, and the heavily-doped N-type layer 15 form a vertical PIN structure. The conventional 2-wavelength light receiving element absorbs wavelengths of 780 nm and 650 nm at a depletion region, which is formed by the P-type epitaxial layer 13 and the N-type epitaxial layer 14, and then converts the wavelengths into electric signals.
However, currently, there is growing demand for image quality that is on the level of high definition (HD) instead of SD and for sound quality that is the same as or superior to that of the DVD in broadcasts. To record and replay images at the HD level and sounds at the DVD level or higher, it is necessary to increase an optical storage density.
A BD (blue-ray disc) technology, in which a short wavelength laser (e.g. wavelength of about 405 nm) is employed and a numerical aperture of an object lens increases to minimize a spot size of a ray, has been studied so as to increase the optical storage density. As shown in FIG. 2, the short wavelength of about 405 nm is mostly absorbed at a distance of 0.1 μm from a surface of a silicon substrate.
However, since the conventional 2-wavelength light receiving element as shown in FIG. 1 has no electric field at a heavily-doped N-type layer, that is, a surface thereof, a movement speed of a carrier moving by diffusion is low, and an electron-hole pair dissipates because of surface recombination (e.g. the carrier is bonded to a dangling bond). Thus, disadvantageously, it is impossible to employ rays having a wavelength of about 405 nm.
An effective light receiving element using a short wavelength of about 405 nm has been studied to avoid the above disadvantages.
FIG. 3 is a sectional view of a conventional light receiving element for receiving blue rays, which is disclosed in Japanese Pat. Laid-Open Publication No. Hei. 9-298308.
As shown in FIG. 3, the light receiving element as disclosed in Japanese Pat. Laid-Open Publication No. Hei. 9-298308 comprises an N-type silicon substrate 21, an N-type epitaxial growth layer 22 formed on the N-type silicon substrate, a plurality of P-type dopant diffusion layers 23 formed in a light receiving part of the N-type epitaxial growth layer 22, and an insulating layer 24 (i.e. SiO2) having recesses. In the light receiving element of Japanese Pat. Laid-Open Publication No. Hei. 9-298308, a carrier, which is formed by absorbing the blue rays of about 405 nm, moves toward an inside instead of a surface of the element to generate electric signals, and thus, advantageously, the element is relatively effective with respect to blue rays having a wavelength of about 405 nm.
However, since the light receiving element of Japanese Pat. Laid-Open Publication No. Hei. 9-298308 has low absorptivity to wavelengths of 780 nm and 650 nm, it is difficult to accommodate CDs or DVDs using the above light receiving element.